Where Q = Flow rate, K = Constant, ρ = Mass density of fluid, ∆P = P1 – P2 pressure type flow meters do not read out directly in either mass or volume flow. Densityįluid density is involved in the determination of either mass flow rate or volume flow rate. In principle, 10:1 to 14:1 flow rangeability and 100:1 to 200:1 DP turndown is the maximum limit while selecting a single Orifice plate as a Flow element. PS: It is also desirable to have the manufacturers always state not only the inaccuracy of their products but also the rangeability/turndown over which that inaccuracy statement is valid. When flow rangeability required above 10:1, the use of two orifice plates of different capacities, two differential-pressure flow transmitters with different ranges, or both is generally recommended. So, flow rangeability can be achievable up to 10:1. However, the standard differential pressure transmitters available in the market with high repeatability and advanced features can generally go up to the turndown of 100:1. (Note: Rangeability of a sensor defines the measurement range over which the error statement, in the units of a percentage of actual reading is guaranteed.) So, flow rangeability (ratio of maximum to minimum flow) can be 14:1. Turndown of differential pressure smart transmitters available in the market can go up to 200:1. Where, Q = Flow rate & ΔP = Differential pressure across the plate. (Explanation of these equations is not included in this article). Selection of Differential Pressure Transmitter Range
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